1. Field of the Invention
The present invention relates to printers in which a disposable member or substance is worn or depleted as part of the printing process, and more particularly to impact printers of the type in which an ink ribbon impacted against a length of print paper is subject to eventual ink depletion or other forms of wear.
2. History of the Prior Art
Many printers utilize a member or substance which is subject to wear or depletion as a part of the printing process. For example, certain non-impact printers utilize toner as part of the printing process. With use of such printers, the toner is eventually depleted and for this reason must be periodically replaced. Many printers of the impact type utilize a member such as an ink ribbon in the printing process. The ink ribbon is repeatedly impacted against a length of print paper or other printable medium by impact elements. The impact elements may each define the shape of a character in the case of full character printers. Alternatively, the impact elements may simply print dots, with characters or other indicia to be printed being formed in dot matrix fashion.
Dot matrix printers may be of the serial type in which a print head containing a number of print wires, needles or other dot forming elements is reciprocated across the width of the print paper with the print wires being selectively actuated to impact the print paper through a length of ink ribbon to print dots on the paper. Dot matrix printers may also be of the line printer type in which a plurality of hammers or other impact printing mechanisms mounted along the length of a hammerbank or other elongated structure within a shuttle assembly are selectively actuated to impact a print paper through a length of ink ribbon and thereby print dots on the paper as the shuttle assembly is caused to undergo reciprocating motion relative to the paper. An example of such a dot matrix line printer is provided by U.S. Pat. No. 3,941,051, "PRINTER SYSTEM", Barrus et al, which patent issued Mar. 2, 1976 and is commonly assigned with the present application.
Many printers such as the type of dot matrix line printer described in U.S. Pat. No. 3,941,051 of Barrus et al utilize a ribbon drive having an opposite pair of spools disposed adjacent opposite ends of a print station defined by the interface between a platen-supported length of print paper and a reciprocating hammerbank. A length of ink ribbon extends through the print station and has the opposite ends thereof wound upon the opposite pair of spools of the ribbon drive. During printing, the opposite spools of the ribbon drive are rotatably driven to provide generally continuous motion of the length of ink ribbon through the print station. Typically, the ribbon moves through the print station at a speed of 2-8 inches per second. When the end of the ribbon is reached, the direction of drive of the spools is reversed, causing the ribbon to move through the print station in the opposite direction. Depending upon the type of ribbon used, the ribbon may undergo many reversals before experience suggests that the ribbon has become worn and should be replaced.
The rate of ribbon wear in impact printers depends on a number of factors including the type of ribbon being used. Ribbons of the so-called single strike type must be handled in such a manner that subsequent impacting of previously impacted areas thereof is minimized or eliminated. Still other ribbons are made of material which does not allow the ink within the ribbon to freely migrate from one area to another. Consequently, when an area of such a ribbon is impacted, there is little if any migration of ink into the impacted area from adjacent areas to help replace the ink depleted therefrom. Ribbons of this type also require special considerations in determining when they are worn and should be replaced.
Many ribbons used in impact printers are made of fabric or other materials which allow relatively free migration of ink into impacted areas of the ribbon from adjacent areas. Such ribbons tend to maintain the quantity of ink therein relatively uniformly distributed as the ribbon is used. Little regard need be given to variations in print density throughout the area of the ribbon because of the relatively good ink migration which tends to maintain the ink distribution uniform throughout the ribbon. Nevertheless, the ink within the ribbon eventually becomes depleted to such an extent that print quality is impaired. When this happens, the ribbon must be replaced.
The nature of ink migration and the problem of eventual ink depletion have been observed by those in the printer industry for some time. In U.S. Pat. No. 4,687,359 of Barrus et al, "COLOR PRINTER", which patent issued Aug. 18, 1987 and is commonly assigned with the present application, ink migration is discussed in connection with a color printer having a multi-color ink ribbon. As discussed in the patent, the transfer of darker color inks to the lighter color zones can produce unwanted ribbon contamination problems. The patent also discusses printing and ribbon advancement techniques for utilizing different areas of the ribbon to maximize ribbon life.
Ribbon type and ribbon composition are just several of the factors involved in determining useful ribbon life. One of the most important factors is the type of printing being done. Thus, the printing of ordinary text comprised principally of characters tends to result in relatively long ribbon life. Bar code printing, on the other hand, represents one of the heaviest uses of ink ribbons and can reduce the useful life of ribbons to a small fraction of the useful life where the printing is principally text printing. The printing of different types of graphics may involve less ribbon use than in the case of bar codes but more than in the case of text printing. Still other types of printing may result in extremely heavy ribbon usage in certain limited areas of the ribbon while the remainder of the ribbon experiences light usage or none at all. Useful ribbon life has been observed to range from as little as several hours to as much as several months in the case of dot matrix line printers of the type described in previously referred to U.S. Pat. No. 3,941,051 of Barrus et al, depending upon the type of printing being done.
There are further examples in the art of arrangements for determining ribbon wear and of adopting measures for extending useful ribbon life. For example, in U.S. Pat. No. 4,619,537 of Do et al, "RIBBON FEED WITH INK DEPLETION COMPENSATION", issued Oct. 28, 1986, an arrangement is described for periodically monitoring print density within given areas of the ink ribbon. When the density within a particular area is determined to exceed a predetermined threshold, the ribbon is then advanced so that another area thereof is used for printing. However, the technique described in the Do et al patent is of limited value with respect to ribbon wear in general, inasmuch as it is restricted to the periodic monitoring of print density within a particular area of the ribbon. Movement of the serial print head is then used to advance the ribbon where necessary so that separate apparatus for advancing the ribbon need not be provided.
Accordingly, it would be advantageous to provide an arrangement for determining ribbon wear or wear or depletion of a similar member or substance as part of the printing process in which all of the printing activity is compiled on a continuous basis to provide an overall indication of the useful life of the ribbon or similar member or substance which remains. Such an arrangement should be capable of not only providing an indication of when the ribbon should be replaced but of actually stopping the printer until ribbon replacement is accomplished where this feature is desired. It should also be capable of determining the actual ribbon life which can reasonably be expected based on factors such as the length of the ribbon and the job rate or other measure of the type of printing to be done. The techniques in accordance with the invention should be adaptable to different printer arrangements such as those lending themselves to the counting of actual dots or characters to be printed as well as those arrangements which facilitate the counting of dot rows or lines of characters.